In packet transmission on wireless physical layer, there are in principle, two diverging requirements which need to be met in order to obtain a desirable quality of transmission: on the one hand it is needed to make the packet transmission reliable, and on the other, to maintain a good level of bandwidth efficiency. In order to make the transmission reliable, redundancy is used. However redundancy is a factor which deteriorates efficiency. That is to say, increase in redundancy, decreases efficiency and vice-versa.
On the other hand, circuit emulation services (CES) allow for the transport of constant bit rate (CBR) flows over a microwave packet radio network. Transmission over microwave packet radio often takes advantage from adaptive coding modulation (ACM) techniques. With ACM, it is possible to use a high modulation scheme in order to have a higher radio bandwidth within a given specific radio channel and switch to low modulation schemes when there is a degradation of radio channel maintaining the radio link in operation using a lower bandwidth. Throughout this description, modulation schemes equal or below 16 QAM, including for example 4 QAM are considered low modulation schemes and modulation schemes equal or over 64 QAM, including for example 128 QAM are considered high modulation schemes.